1. Technical Field
The present invention relates to a liquid developer, a method of manufacturing a liquid developer, and an image forming apparatus.
2. Related Art
A developer for developing an electrostatic latent image formed on a latent image carrier is classified into one for a method using a dry toner, which is composed of a material containing a colorant, such as a pigment or the like, and binder resin, in a dry state, and another for a method using a liquid developer, in which a toner is dispersed in an electrical insulation carrier liquid (insulation liquid).
In the method using such a dry toner, since a solid state toner is handled, it is advantageous in handleability. Meanwhile, there are many problems in view of an adverse affect of toner powder on a human body, contamination by dispersion of toner, and uniformity when the toner is dispersed. Further, in such a dry toner, since aggregation of toner particles is likely to occur, it is difficult to obtain toner particles each having a sufficiently small size. Further, it is difficult to form a toner image with high resolution. In addition, when the sizes of the toner particles are comparatively small, the above problems by the toner powder drastically appear.
Meanwhile, in a developing method using such a liquid developer, since aggregation of toner particles in the liquid developer can be effectively prevented, fine toner particles can be used and a binder resin having a low softening point (a low softening temperature) can be used. As a result, the developing method using the liquid developer has such advantages as good reproducibility of an image having thin lines, good gray-scale reproducibility, and excellent color reproducibility. Further, the developing method using the liquid developer is also a method of forming an image at high speed.
However, since an insulation liquid used in the known liquid developer mainly contains petroleum-based carbon hydride, there is concern that the insulation liquid may have an adverse affect on environment if it flows out of an image forming apparatus.
Further, usually, when the liquid developer is used, the insulation liquid is adhering to a surface of each toner particle upon fixing. In the known liquid developer, there is a problem in that such an insulation liquid adhering to the surfaces of the toner particles lowers a fixing strength of the toner particles. In order to improve the fixing strength of the toner, a method that heats the toner particles at a comparatively high temperature for hours to fix the toner particles has been considered. However, this method cannot satisfy demands for high-speed image formation and power saving.
In order to solve the above-described problem, JP-A-11-212035 discloses a method that uses natural fatty oil as the insulation liquid.
A liquid developer described in JP-A-11-212035 uses an oxidization polymerization reaction of the natural fatty oil to improve a fixing property. However, since the natural fatty oil has low permeability for a recording medium, it is difficult to obtain a sufficiently high fixing strength.